For electronic signal filter applications that require magnetic isolation shielding between different filter sections, isolation shields are typically soldered to the circuit board. After the circuit board sub-assembly is inserted into an electronic signal filter housing (which is typically grounded), the isolation shields are soldered to the housing to provide a ground connection between the circuit board and the filter housing. There are some electronic signal filter applications, however, that do not require magnetic isolation shielding, and thus, do not include isolation shields that can also be used to provide the required ground connection.
In electronic signal filter applications where magnetic isolation is not required, ground straps have instead been used to provide the required ground connection between the circuit board and the filter housing. One example of such a ground strap is shown in FIG. 1.
The circuit board sub-assembly 130 shown in FIG. 1 includes a ground strap 10 and a notched circuit board 100. The ground strap 10 is an arched structure including a flattened upper portion 15 interposed between arch portions 14a and 14b. As shown, the upper portion 15 of the ground strap 10 is substantially parallel to the plane of the circuit board 100, that is, parallel to both the upper surface 101 and the lower surface 102 of the circuit board 100. The arched portions 14a, 14b respectively include a shoulder portion 13a, 13b proximate the respective terminal ends thereof. The shoulder portions 13a, 13b extend inwardly as shown in FIG. 1 in a direction that is substantially parallel to the plane of the circuit board 100. A pair of support arms 13c, 13d extend from a respective shoulder portion 13a, 13b in a direction that is also substantially parallel to the plane of the circuit board 100, such that the support arms 13c, 13d are substantially inwardly extending extensions of the respective shoulder portions 13a, 13b. 
Proximate the shoulder portions 13a, 13b, the terminal end portions of the ground strap 10 are again bent to form a pair of leg portions 12a, 12b that extend from a respective shoulder portion 13a, 13b in a direction (e.g., downward) that is substantially perpendicular to the plane of the circuit board 100. The leg portions 12a, 12b are also bent to form a respective foot portion 11a, 11b that extends in a direction that is substantially perpendicular to the direction of the leg portions 12a, 12b (e.g., inwardly as shown in FIG. 1) and that is also substantially parallel to the plane of the circuit board 100.
As shown in FIG. 2, the circuit board 100 of FIG. 1 is merely one of a plurality of interconnected circuit boards 100 that are formed in a sheet of circuit board material such that the circuit boards 100, 100′ are attached via retention tabs 121a, 121b (121a′, 121b′) to form an array 120. As shown in FIGS. 1 and 2, each circuit board 100 includes an upper surface 101, a lower surface 102, a first lateral side 103, an opposed second lateral side 104, a first end 105 and an opposed second end 106. As shown in FIG. 2, while the circuit boards 100 remain in the array 120 via the retention tabs 121a, 121b, the first end 105 and the second lateral side 104 are defined by singulation channel 122, and the second end 106 and the first lateral side 103 are defined by singulation channel 123. Singulation channel 122 is separated from singulation channel 123 by retention tab 121a proximate the intersection point of the first lateral side 103 and the first end 105 of the circuit board 100, and by retention tab 121b proximate the intersection point between the second lateral side 104 and the second end 106 of the circuit board 100.
In the array 120, as shown in FIG. 2, a circuit board 100′ is located immediately adjacent each circuit board 100, sharing a common singulation channel. For example, in FIG. 2, circuit board 100′ includes a first lateral side 103′, an opposed second lateral side 104′, a first end 105′ and an opposed second end 106′. While the circuit boards 100′ remain in the array 120 via the retention tabs 121a′, 121b′, the first end 105′ and the second lateral side 104′ are defined by singulation channel 124, and the second end 106′ and the first lateral side 103′ are defined by the common singulation channel 122 that is shared with the adjacent circuit board 100 as shown. Singulation channel 122 is separated from singulation channel 124 by retention tab 121a′ proximate the intersection point of the first lateral side 103′ and the first end 105′ of the circuit board 100′, and by retention tab 121b′ proximate the intersection point between the second lateral side 104′ and the second end 106′ of the circuit board 100′.
A pair of notches 110, 110 are provided in the first and second lateral sides 103, 104 of the circuit board 100. The notches 110 are each defined by a pair of parallel notch sides 111 that extend inwardly from the peripheral edges of the first and second lateral sides 103, 104 toward a respective terminal end in a direction that is perpendicular to the first and second lateral sides 103, 104 and by a notch base 112 that extends between the respective terminal ends of the notch sides 111 in a direction that is parallel to the first and second lateral sides 103, 104. The parallel notch sides 111 have a length that is approximately 0.030″, and each notch base 112 has a length that is slightly longer than the width of the foot portions 11a, 11b of the ground strap 110. The notch bases 112 and parallel notch sides 111 of each circuit board 100 are plated with a conductive plating material.
A plurality of the ground straps 10 of FIG. 1 are attached to the circuit boards 100 of the array 120 in the manner shown in FIG. 3. That is, a first ground strap 10 is attached to a first circuit board 100 of the array 120 by positioning the foot portion 11a proximate the lower surface 102 of the circuit board 100 in the vicinity of the notch 110 on the first lateral side 103 of the circuit board 100. The ground strap 10 is positioned and moved laterally (i.e., Y-axis assembly movement) and slightly vertically (i.e., Z-axis assembly movement) toward the first lateral side 103 of the circuit board such that the support arm 13c is positioned on the upper surface 101 of the circuit board 100 and the upper surface of the foot 11a is positioned on the lower surface 102 of the circuit board 100. The Y-axis lateral positioning continues until the leg portion 12a is substantially flush against the notch base 112. The ground strap 10 is then essentially stretched up and over the circuit board 100, in both the Y and Z-axis directions, until the upper surface of the other foot portion 11b is positioned under the lower surface 102 of the circuit board 100. The ground strap 10 is then resiliently snapped into position such that the upper surface of the foot portions 11a, 11b contact the lower surface 102 of the circuit board 100, the support arms 13c, 13d contact the upper surface 101 of the circuit board 100, and the leg portion 12b is substantially flush against the notch base 112 on the second lateral side 104 of the circuit board 100. A bottom view of the assembled circuit board sub-assembly 130, including the circuit board 100 with the ground strap 10 attached thereto is shown in FIG. 4.
Subsequent ground straps 10 are then attached to adjacent circuit boards 100 of the array 120 in a similar manner. After the ground straps 10 are properly assembled onto the array 120 and the array 120 is wave soldered, the individual circuit boards sub-assemblies 130 themselves (which also include a plurality of discrete electronic components that are not shown) are singulated from the array 120 by severing the retention tabs 121a, 121b. The individual circuit board sub-assemblies 130 are then inserted into various electronic equipment, such as CATV filter housings, and a ground connection between the circuit board 100 and the filter housing is provided by soldering a portion of the ground strap 10 to the filter housing through a notch provided in the filter housing member.
There are, however, several drawbacks associated with using the circuit board sub-assembly 130 including the ground strap 10 and the notched circuit board 100 shown in FIGS. 1–5.
First, it is difficult to provide the required conductive plating material on the notch sides 111 and the notch base 112 defining the notches 110 in the thickness direction of the circuit board 100 since the notches 110 are typically punch formed. That is, the punch formed surfaces of the notches 110 are not smooth, as compared to drilled or routed surfaces, and that roughened surface structure, in combination with the position on the peripheral edges of the lateral sides of the circuit boards 100, are not conducive to efficient and effective plating.
Second, due to the fact that the circuit boards 100 are closely positioned in the array 120, that is, spaced apart from one another by little more than the widths of the singulation channels 122 and 123 and possibly a small amount of circuit board material therebetween, there is only a minute clearance (on the order of 0.100″) between the peripheral edges of adjacent circuit boards 100, as shown in FIG. 5. Further, since the shoulder portions 13a, 13b of the ground straps 10 extend laterally outwardly a distance beyond the peripheral edges of the first and second lateral sides 103, 104 of the circuit boards 100 toward other adjacent ground straps 10, the clearance between adjacent sub-assemblies 130 is further limited. This very close proximity presents difficulties when sequentially assembling subsequent ground straps 10 on the array 120, since each ground strap 10 must be stretched both upwardly (Z-axis) and outwardly (Y-axis) in order to be positioned in and retained by the notches 110 in the circuit boards 100. That is, the required multi-directional-axis assembly steps are more complicated and time consuming than single- axis assembly steps. Additionally, the close proximity of adjacent ground straps further complicates the process in that a high degree of precision is required to ensure proper assembly of each ground strap and to avoid causing damage to adjacent ground straps during the assembly process.
The structure of the circuit board sub-assembly 120 causes another problem in that solder wicking tends to be promoted between adjacent ground straps 10 when the array 120 is wave soldered. For example, referring to FIG. 5, solder from the bath tends to travel (wick) up the outer surfaces of the leg portions 12a, 12b of the ground strap 10, and the outer surfaces of the leg portions 12a′, 12b′, such that solder ends up being present between the bulbous portion of shoulder 13b of the ground strap 10 and the adjacent bulbous portion of shoulder 13a′ of the ground strap 10′. In order to prevent such wicking, a plurality of plastic insulator members (not shown) are provided in the clearance between adjacent ground straps before the array 120 is wave soldered. Although the plastic insulator members effectively prevent the adjacent ground straps from being soldered together as a result of the aforementioned wicking, these plastic insulator members constitute additional parts and additional assembly steps must be performed to insert the insulation members before the array is wave soldered and after the array is wave soldered, prior to singulation, to remove the insulator members. In that manner, the costs, with respect to both time and parts, are increased.
The circuit board sub-assembly 230 shown in FIG. 6, including a ground strap 20 provided on a slotted circuit board 200, was developed to address the aforementioned drawbacks associated with the circuit board sub-assembly 130. As shown in FIG. 6, the ground strap 20 is an arched structure including a flattened upper portion 25 interposed between arched portions 24a and 24b. The upper portion 25 of the ground strap 20 is substantially parallel to the plane of the circuit board 200, that is, parallel to both the upper surface 201 and the lower surface 202 of the circuit board 200. The arched portions 24a, 24b respectively include a shoulder portion 23a, 23b proximate the respective terminal ends thereof. The shoulder portions 23a, 23b extend inwardly as shown in FIG. 6 in a direction that is substantially parallel to the plane of the surfaces 201, 202 of the circuit board 200.
Proximate the shoulder portions 23a, 23b, the strap 20 is again bent to form a pair of substantially perpendicular leg portions 22a, 22b that extend from a respective shoulder portion 23a, 23b in a direction (e.g., downward) that is substantially perpendicular to the plane of the surfaces 201, 202 of the circuit board 200. The leg portions 22a, 22b are also slightly bent to form a respective hook portion 21a, 21b that extends in an angled direction, e.g., outwardly as shown in FIG. 6, from the respective terminal ends of the ground strap 20.
Like the circuit board 100 shown in FIG. 2, the circuit board 200 of FIGS. 6–10 is merely one of a plurality of interconnected circuit boards 200 that are attached via retention tabs 221a, 221b in an array 220. Each circuit board 200 includes an upper surface 201, a lower surface 202, a first lateral side 203, an opposed second lateral side 204, a first end 205 and an opposed second end 206.
As shown in FIG. 7, while the circuit boards 100 remain in the array 220 via the retention tabs 221a, 221b, the first end 205 and the second lateral side 204 of the circuit board 200 are defined by singulation channel 222, and the second end 206 and the first lateral side 204 are defined by another singulation channel 223. Singulation channel 222 is separated from singulation channel 223 by retention tab 221a proximate the intersection point of the first lateral side 203 and the first end 205 of the circuit board 200, and by retention tab 221b proximate the intersection point between the second lateral side 204 and the second end 206 of the circuit board 200.
In the array 220, as shown in FIG. 7, a circuit board 200′ is located immediately adjacent each circuit board 200, sharing a common singulation channel 222. For example, circuit board 200′ includes a first lateral side 203′, an opposed second lateral side 204′, a first end 205′ and an opposed second end 206′. While the circuit boards 200′ remain in the array 220 via the retention tabs 221a′, 221b′, the first end 205′ and the second lateral side 204′ are defined by singulation channel 224, and the second end 206′ and the first lateral side 203′ are defined by the common singulation channel 222 that is shared with the adjacent circuit board 200 as shown. Singulation 222 is separated from singulation channel 224 by retention tab 221a′ proximate the intersection point of the first lateral side 203′ and the first end 205′ of the circuit board 200′, and by retention tab 221b′ proximate the intersection point between the second lateral side 204′ and the second end 206′ of the circuit board 200′.
Unlike the circuit board 100 shown in FIG. 2, however, each circuit board 200, 200′ of FIGS. 6–10 includes a pair of slots 210 (210′) formed therein proximate a respective one of the first and second lateral sides 203, 204 thereof. Each slot 210 is essentially an elongated hole that includes a first rounded end 211, an opposed second rounded end 213, and a pair of parallel slot sides 212a, 212b extending therebetween. The slot sides 212a, 212b are spaced apart from each other by a distance of about 0.030″, and the outer slot sides 212a, 212b are spaced a distance of about 0.030″ from the peripheral edges of the first and second lateral sides 203, 204 of the circuit board 200.
A plurality of the ground straps 20 of FIG. 6 are attached to the circuit boards 200, 200′ of the array 220 in the manner shown in FIG. 8. Using only Z-axis manufacturing techniques, the arched portions 24a, 24b of the ground strap 20 are compressed, for example, by a lateral pincer motion of a Z-axis type robotic arm, and the hook portions 21a, 21b are downwardly inserted into the slots 210 until the terminal ends of the hook portions 21a, 21b are positioned under the lower surface 202 of the circuit board 200. When the compressive force is robotically released, the arched portions 24a, 24b expand outwardly and the leg portions 22a, 22b contact the outer slot sides 212a within each slot 212. The hook portions 21a, 21b effectively engage the lower surface 202 of the circuit board 200 and extend a distance beyond the outer slot sides 212a toward the peripheral edges of a respective first or second lateral side 203, 204 of the circuit board 200.
As shown in FIGS. 6 and 9, for example, the outer slot sides 212a of the slots 210 are inwardly spaced a distance from the edges of the lateral sides 203, 204 of the circuit board 200 such that the shoulder portions 23a, 23b contact the upper surface 201 of the circuit board 200 between one of the outer slot sides 212a and a respective lateral side 203, 204 of the circuit board 200. The circuit board 200 is effectively sandwiched between the shoulder portions 23a, 23b and the hook portions 21a, 21b, and the leg portions 22a, 22b exert a force on the outer slot sides 212a to provide a degree of anti-rocking stability for each sub-assembly 230.
In that manner, the circuit board sub-assembly 230 including ground strap 20 in combination with the slotted circuit boards 200, 200′ provides a degree of anti-rocking stability and substantially eliminates Y-axis insertion assembly steps, which offers a significant improvement over the ground strap 10 and notched circuit boards 100, 100′ of FIGS. 1–5.
Further, as shown in FIG. 10, since the slots 210 are spaced inwardly from the peripheral edges of the lateral sides 203, 204 of the circuit board 200, a sufficient clearance is maintained between the shoulder portion 23b of ground strap 20 and the shoulder portion 23a′ of ground strap 20′ shown in FIG. 10. Further, since the leg portions 22a, 22b are located within (e.g., surrounded by) the slots 210, the outer surfaces of the leg portions 22a, 22b are not directly exposed to the solder in the bath and the aforementioned wicking phenomena, described above with respect to FIG. 5, does not occur. Accordingly, there is no need to provide and position additional plastic insulator pieces between adjacent ground straps 20 before wave soldering the array 220, which, in turn, reduces the amount of time and materials, and thus the costs, required to produce the circuit board sub-assemblies 230.
Moreover, since the slots 210 are inwardly spaced from the peripheral edges of the lateral sides 203, 204 of the circuit board 200, and since the slots 210 shown in FIG. 11 are formed in the sheet of circuit board material 2 by peck drilling a series of overlapping holes in positions corresponding to the proper location for each circuit board 200 of the array 220 (see also FIG. 7), the slots 210 can easily be plated. This eliminates the aforementioned plating difficulties experienced in connection with the notched circuit boards 100 and provides yet another time saving advancement over the previous ground strap 10 and circuit board sub-assembly 130.
Although the ground strap 20 essentially addresses and corrects the aforementioned problems associated with the ground strap 10, drawbacks remain when using the circuit board sub-assembly 230 including the ground strap 20 and the slotted circuit board 200. For example, due to the elongate structure of the slots 210 and their proximity to the peripheral edges of the lateral sides 223, 224 of the circuit board 200, the slots 210 tend to experience deformation when the singulation channels 222, 223 defining the periphery of the circuit boards 200 are punch formed.
That is, when the singulation channels 222, 223 are punched, some of the circuit board material 2 tends to encroach upon and deform the previously peck-drilled slots 210. More specifically, the outer slot sides 212a of the slots 210 can be warped inwardly or otherwise compressed such that the proper portions of the ground strap 20 will not fit therein as intended without first routing out the slot 210. This additional routing operation is yet another slot formation step that further increases production time and costs, and one that must be specifically directed to those slots 210 that actually experience deformation.
In an effort to address this slot deformation problem, the following solution was implemented. That is, after the pairs of slots 210 are formed in their proper locations on the circuit board material 2, as shown in FIG. 11, a second set of juxtaposed peck-drilled slots 215 are formed in positions corresponding to the intended locations of the singulation channels 222, 223, immediately adjacent the slots 210, as shown in FIG. 12. In that manner, since none of the circuit board material 2 is present in the location of the second set of peck drilled slots 215 when the circuit board material 2 is punched to form the singulation channels 222, 223, the aforementioned slot deformation is reduced.
Although targeted subsequent routing of the slots 210 is essentially avoided in this manner, forming the second set of peck drilled slots 215 prior to punch forming the singulation channels 222, 223 still requires an additional, precision manufacturing step that would be desirably avoided.
Additionally, the structure of the slotted circuit board 200 subjects the circuit board sub-assembly 230 to other stress defect/failure factors. That is, the shape of the slots 210 also presents drawbacks due to the proximity to the edges of the circuit board, the elongate configuration, and the manner in which the ground straps 20 apply pressure on the outer slot sides 212a thereof, as described above. Further, although the slots 210 assume less of the total surface area of the circuit board 200 than the notches 110, it would be even more desirable to provide a ground strap that could be assembled to a circuit board in a manner that requires even less circuit board surface area.
Thus, it would be desirable to provide a ground strap that overcomes all of the above drawbacks associated with prior art ground straps. It would be desirable to provide a ground strap that can be assembled to a circuit board while requiring only a minimal amount of circuit board surface area, a ground strap that provides a circuit board sub-assembly having improved strength and durability, and a ground strap that facilitates overall improved manufacturing efficiency.